I am reading Anthology for Music in the Twentieth and Twenty-First Centuries, and on page 173 I get stuck in understanding this sentence:
In some cases national and political connotations were an explicit factor in the creative process; in other cases a composer’s works or style were co-opted after the fact, sometimes for very different purposes than the composer may have intended.
The author says that the creative process accelerated in the rapidly changing interwar years because old structures became inviable. I thought that due to such explicit factors composers's works or style were strongly affected by dimensions that themselves had not intended.
Am I right? How to embed the phrase "co-opted after the fact" into my understanding in this context? Could anyone please help explain the phrase in depth to some extent? I can find little about that phrase on the Internet myself. Thank you.